In a wavelength division multiplexing (WDM) transmission system in a related art, a plurality of optical signals having wavelengths different from each other may be multiplexed and transmitted at the same time. Further, in a related art, presence or absence of a failure in an optical path may be decided based on a result of comparison of alarm states of an optical path. Further, in another related art, alarms detected in a WDM transmission apparatus used in a WDM transmission system may be aggregated by an aggregation apparatus and transferred to a network management server.
Examples of the related art include Japanese Laid-open Patent Publication No. 2008-244823.